The invention relates to welding wire, and particularly to welding wire for welding low-alloy high-strength steel, and more particularly to welding wire for welding low-alloy high-strength steel for the construction of electric towers.
The electric towers (electric power steel towers) are widely used in setting up long-distance high-voltage electric cables for transmitting high-voltage, for example, higher than 100 kV. In setting up the high-voltage electric cables, there is a required height to the electric tower, because the lowest height is decided by the span of the high-voltage electric cables between two the electric towers and by the ground clearance height of the high-voltage electric cables.
For a long time, the electric towers are constructed by using low-strength steel and there are no coating layers on the surfaces of the electric towers. However, in 2008 the large-area snow damage was occurred in the south of China and the long duration of the snow disaster caused aggregation of ice on the electric cables. The thickest icecap on the electric cables even exceeded 50 mm Many electric towers were finally collapsed by the tension of the electric cables and the pressure produced by the icecap on them, which in turn caused the break of electricity transmission and brought severe difficulty to human life. The specialists later analyzed the causes of the collapse and found that one of the causes was that the load capacity of the electric towers in the south of China became too weak to sustain the load of the electric towers when the cables were frozen with icecaps. To enhance the capability against disaster (including snow disaster), there is a need to improve the load capacities of the electric towers.
China is now planning to establish large energy bases, that is, to generate large amount of electric power by selecting solar, wind power or nuclear energy in suitable areas and to transmit the electric power from the large energy bases to other locations that use the electric power. These large energy bases may be far away from the locations that use the electric power. It is known that the higher the transmitting voltages are, the longer the transmitting distances are. To increase transmitting distances of the electric power, the method of raising transmitting voltages is commonly used. The problem associated with raising transmitting voltages is that it can adversely affect the environment in transmitting the electric energy; especially the radiation generated may have negative effect on the health of human beings. Thus, when transmitting electric power with high voltages and ultra-high voltages, the distance between the electric cables and the ground is required to be longer to avoid negative effect to human beings, thus requiring electric powers sufficiently high. However, the higher the electric powers are, the heavier the loads are, which in turn requires higher load capacity to electric towers. To increase the height of the electric towers, it requires the components, from which the electric towers are assembled, to have higher load capacity.
In addition, to the electric towers with same height, the larger the tower base is, the lower the strength requirement to the electric tower assembly components is, because when the tower base gets larger, the electric tower assembly components can be made larger to have larger load capacity. On the other hand, when the tower base is smaller, the electric tower assembly components have to be made smaller and the strength requirement to the electric tower assembly components are higher. However, comparing with the electric tower with lager tower base, the electric tower with smaller tower base occupies less land. For decreasing land occupancy, there is also a need to increase load capacity so that the electric tower can be made smaller.
The outdoor (or field) long-term load capacity of an electric tower depends on two factors. One factor is the strength of the steel used in constructing the electric tower because when the strength of the steel is higher, the load capacity of the electric tower is larger. The other factor is the life-span of the assembly components used in constructing the electric tower. The electric towers are exposed to the environment for a long time and can be damaged by temperature, wind and precipitations in the atmosphere. After longtime use, if no protection, the steel of the electric tower can be corroded and the load capacity of the corroded steel will decrease. Thus, there are two ways to increase the load capacity of an electric tower. One is to use low-alloy high-strength steel as construction materials and the other is to put coatings such as galvanization on the surfaces of the assembly components that construct electric tower, to prevent the damage and corrosion to the electric tower. Because the conventionally used materials and methods for constructing electric towers cannot meet the requirements due to the development of the electric industry, there is a need to use low-alloy high-strength steel (such as Q420 steel) to construct electric towers with the requirement to galvanize the surfaces of the electric tower assembly components.
Conventionally, the electric industry uses solid welding wire to weld electric tower assembly components. After observing and researching the conventional method and technology of constructing the electric towers, the inventors of the present invention found they have at least two shortcomings by using solid welding wire to weld low-alloy high-strength steel assembly components. One shortcoming is that many welding slags are firmly bonded at the welding beads (or selding seams). It is difficult and time consuming to clean the welding slags and grind the welding beads. The other shortcoming is that even after cleaning the welding slags and grinding the welding beads, they are still rough and not smooth. It is difficult and costly to galvanize the welding beads and the quality of the galvanizing coatings on the welding beads is not good. Moreover, it is very difficult to make the thickness of the coatings on the welding beads consistent with that on the adjacent steel surfaces.